Radio frequency distribution system



Patented July 2, 1935 UNITED STATES PATENT OFFICE SYSTEM Alva R. Hopkins, Merchantville, N. J., assgnor to Radio Corporation of America, a corporation of Delaware Application May 10, 1932, Serial No. 610,424

5 Claims.

My present invention relates to radio frequency distribution systems, and more particularly to a radio frequency distribution system of the type wherein radio broadcast signals are distributed to a plurality of independent receivers.

There has been disclosed by C. C. Shumard in application Serial No. 518,093 led February 25, 1931 a radio frequency distribution system wherein it is possible to distribute radio broadcast programs to a plurality of independent receivers throughout a habitable structure, such as a hotel, apartment house, office building, or through a Steamship, train and t The said application discloses a central collecting and amplifying station wherein radio broadcast signals are collected and aperiodically amplified, the amplified signals being then transmitted over a shielded radio frequency transmission cable. The cable is lead through the various receiving points of the structure, and at each receiving point there is provided an outlet so that broadcast reception may be had by merely connecting the antenna and ground conductors of a radio receiver to the proper terminals of the outlet. In such a system, however, each receiver is an independent unit, and where it is desired to utilize alternating current to energize the various circuits of each of these independent receivers, it is necessary to provide the usual rectifier and lter arrangement with each independent receiver.

Now, I have devised an improved type of radio frequency distribution system wherein the enerndent is Qcateimhaaentrauta; tion it being merely necessary in the use of this improved system to plug in the usual antenna, ground connections in order to energize the various electrical circuits of each independent receiver unit.

Accordingly, it may be stated that it is one of the principal objects of the present invention to provide a radio frequency distribution system, wherein amplified broadcast signals are distributed from a central station to a plurality of independent receiver units, a voltage supply source being located at the said central station, which source is so associated with the radio frequency transmission line that the said line performs the double function of distributing the broadcast signals to the said receivers, and simultaneously provides a connecting link between the aforementioned voltage source and the circuits of each receiver which is connected to the transmission line.

Another object of the present invention is to (Cl. Z50-9) provide a shielded radio frequency transmission cable between a central station adapted to amplify broadcast signals, and a plurality of extension receiver units, and a voltage supply source for the circuits of said units arranged at the central station so that its output is impressed upon the cable in such a manner that connection of any of said units to said cable results in supply of broadcast signals, and energization of the circuits of each receiver unit.

Still other objects of the present invention are to improve generally the simplicity and efficiency of radio frequency distribution systems, particularly adapted for dwellings housing a plurality of independent receiver units, and to especially provide a. system wherein each of the receiver units need not be provided with a rectier or filter circuit, even if the voltage supply source is an alternating current source, thus providing a system which is not only durable and reliable in operation, but economically manufactured and installed.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicatcd diagrammatically one circuit arrangement for carrying my invention into effect.

Referring now to the accompanying drawing there is diagrammatically shown a radio frequency distribution system of the type disclosed in the aforementioned Shumard application. It is only believed necessary to disclose the essential features of this system, as the present invention is readily applicable to any other type of radio frequency distribution system. The aforementioned Shumard system comprises central station radio frequency amplification equipment, usually located at some central point of a dwelling. For example, the area bounded by the dotted lines C in the drawing is supposed to represent a central station room in an apartment house or hotel, such as a room adjacent the roof of the house, the usual outdoor grounded antenna I being utilized to collect the broadcast energy and feed it into an aperiodic amplifier 2. Of course, in the case of a mobile structure, such as a Steamship, the centra1 station room need not necessarily be adjacent the antenna, but may be some other room which is conveniently located for the distribution of the amplified radio frequency signals to the various rooms, or cabins, where the various independent receivers are situated. The aperiodic amplifier 2 may comprise one or more stages of amplification, the essential characteristic of this amplifier being its substantially uniform response to all frequencies amplified by it.

'I'he amplified energy is impressed upon the input of the radio frequency transmission cable 3 by means of any desired type of coupling, as at Mi, the secondary of the coupling having its high potential terminal connected to the high potential conductor 4 of the cable 3, while the low potential terminal of the said secondary is connected to the low potential, or ground, strip 5 of the cable. A condenser 6, of high impedance to unidirectional current and low impedance to alternating current, is connected in series in the said secondary circuit between the conductors 4 and 5. The construction of the cable 3 is fully disclosed in the aforementioned Shumard application, and need only be described herein as comprising a low impedance cable of substantially uniform loading.

The physical structure of the cable consists of an inner conductor 4 (preferably of copper) surrounded by insulation 1, a ground strip 5 (also preferably of copper) being in contact with a portion of the periphery of the insulation layer 1. A metallic sheath 8 (preferably of lead) surrounds the elements l., I and 5, and is in contact with the ground strip 5 along a portion of its inner periphery. In this way the cable 3 is not only shielded against electrical interference, but is flexible and readily adapted to wiring. It will be noted that the end of the cable adjacent the coupling M1 has been shown in cross section in order to clearly demonstrate the construction of the cable, the remainder of the cable being represented, to preserve simplicity of description, by single dotted lines.

The flexible cable 3 is wired throughout the structure in any desired manner, the cable being led through various rooms of an apartment, or through different apartments, or flexible cable branches may be connected to the main cable, the branches being led into various apartments. In the accompanying drawing there is shown in detail the construction of an extension receiver unit, the dotted lines El designating a particular apartment housing the extension receiver unit shown in detail. The dotted lines E2 represent another room, or apartment, housing an independent extension receiver unit, whose construction will be understood to be identical with the one housed in the area E1 and now to be described.

The outlet connection from the cable 3 to each extension receiver unit preferably comprises a short lead 9 connected at one end to the conductor 4 of the cable 3, and terminating at its other end in an outlet box (not shown) but usually designated by the letter A to indicate that it represents the antenna terminal of the cable. A protected polarity plug connector (so protected because of the direct current voltage) may also be used. The short lead I2 connects the ground terminal, designated by the letter G, of the outlet box to the ground strip 5 of the cable, it being understood that the ground strip is in contact with the outer metallic sheath 8, the latter usually being grounded, as at I3. This outlet construction between the cable and the outlet box of each apartment is the same all along the cable, and, therefore, similar numerals are employed to represent corresponding structural elements in connection with the receiver unit in the area E2.

The cable 3 is preferably terminated by connecting a terminating resistor I4 between the conductor 4 and the ground strip 5, a condenser I5 being connected in series with the resistor I4, the condenser having a low impedance to the radio frequency currents but having a high impedance to uni-directional current. 'I'he value of the resistor I4 should be equal to the impedance of the line, (50 ohms in case of the Shumard cable). The ground strip 5 is in contact with the sheath 8, the latter preferably being grounded as at I4 to establish, if desired, the strip 5 at ground potential for the entire length of cable.

In order to provide a potential supply source for the various circuits of the amplifier 2, there is located at the central station a rectifier I6 having its output connected to any conventional and well known filter circuit I'I, with voltage regulator means I'I' included, it being understood of course that this arrangement is employed when the potential source I8 is the usual 110 volt, 60 cycle alternating current power line. 'I'he positive side of the filter output is connected by a lead I9 to the amplifier 2, while the negative side of the filter output is connected by a lead I9' to the cathode return circuit of the amplifier. It is not believed necessary to show in detail the circuits of the amplifier 2, since such circuits are well known to those skilled in the art.

The present invention essentially comprises the feature of supplying proper potentials to the various circuits of the independent extension receiver units from the potential supply source I5, I1, I1', I8 located at the central station. This is accomplished by connecting a lead 20 between the positive side of the filter output I'I and one side of the condenser 5, and similarly connecting a lead 2I between the negative side of the filter output and the opposite side of the condenser 6.

Thus, it will be seen that there not only exists a radio frequency potential difference between the conductors 4 and 5 of the cable 3, but that there simultaneously exists a uni-directional current potential difference between these two conductors, and that the leads 9 and I2 connected to each outlet box of a receiver unit are at similar potential differences. It will also be observed that the insertion of condenser I5 in series with the terminating resistance I4 eectively prevents the flow of uni-directional current through the conductors 4 and 5 when no extension receiver units are electrically connected to the cable.

The extension receiver unit shown in detail in the drawing comprises in its essential features a radio frequency amplifier stage including a screen grid tube 22, and a detector stage comprising a triode 23, the output circuit of the detector tube 23 being coupled, as at M2, to any desired type of loudspeaker, or headphones if desired. Each of tubes 22 and '23 are shown as of the indirectly heated cathode type, the heating filaments of these tubes being connected in parallel across the secondary of the usual filament transformer M3, the primary of the latter being connected to the usual 110 volt alternating current supply line. In case of direct current installations the filaments of the tubes may be connected directly to the 110 volt line through suitable resistors, as is well known in the prior art. A tunable resonant circuit is connected between the grid and cathode of tube 22, the resonant circuit including the inductance 24, and the variable condenser 25, the coil 24 being coupled to a primary coil 26 having one end thereof connected, through a blocking condenser 21 of' high impedance to uni-directional current, and resistor 4| to the antenna terminal A of the lead 9, the ground terminal G of the lead I2 being connected by a lead I2 to the low potential side of the primary coil 29. Radio frequency by-pass condensers 28 are connected between the cathode and grid return and the anode return circuit and cathode of tube 22.

The input circuit of the detector tube 23 includes an inductance coil 29, shunted by a Variable tuning condenser 30, the coil 29 being coupled to the primary coil 3|, disposed in the anode circuit of tube 22, to receive the amplified radio frequency energy. The rotors of the variable condensers 25 and 3|) are mechanically connected in any desired and well known manner, as by a mechanical uni-control arrangement 32, so that both resonant circuits may be tuned to select a desired radio broadcast frequency. Radio frequency by-pass condensers 32 are connected between the grid and cathode, and the anode and cathode of tube 23. 'I'he anodes of each of tubes 22 and 23 are supplied with suitable positive potential through leads 33, the common lead 34, the radio frequency choke 35, and the lead 36 connected to the antenna outlet A of the lead 9.

A resistor 31 is connected between the screen grid of tube 22 and the lead 33 to provide a suitable screen grid potential. The cathodes of tubes 22 and 23 are connected to the lead I2', the latter being directly connected to the ground conductor strip 5 of the cable 3 through leads 38, 39 and 4|). 'I'he cathode of tube 22 includes in its negative leg a grid biasing resistor 4|', preferably made adjustable to provide a volume control means, and the negative leg of the cathode of tube 23 includes a grid biasing resistor 42 to supply the grid of the detector tube 23 with suiiicient bias to operate the tube 23 as a detector employing anode rectification, it being understood that proper design of the constants of this type of detector results in a detector output of sufficient power to operate a loudspeaker. However, it is obvious that additional audio amplification may be added if more audio power is desired.

It will now be seen that the potential supply for the various circuits of the extension receiver unit is derived from the cable 3, and that the latter in turn comprises such a supply source by virtue of the connection to it of the potential output of the filter located at the central station. Of course, it will be understood that by proper design of the rectifier I6 and filter the proper uni-directional current potentials can be supplied over the cable 3 to the extension receiver units. Again, it will be observed that even though alternating current sources are utilized at the central station, and at each extension receiver unit, there is no need to employ expensive rectifier and filter circuits at the extension units. The present system is not limited to the use of filtered alternating current supply at the central station C, but can be readily used in direct current installations. In the latter case the central power supply unit consists of a motor generator set With a proper filter circuit.

Of course, the receiver units may be supplied in one or more models, each design to take care of different audio requirements. For example, the detected output of a receiver unit may be amplified by one or more stages of audio frequency amplification if desired. #Agigglfgllgplwllenn so-callegniragqpillcwspre to be operated from a receiver unit output, the receiver unit could be Examiner designed to deliver less audio power than would be necessary to operate loudspeakers.

It is believed that the operation of the systern described in this application will be clearly understood from the aforegoing description and the drawing. It is to be particularly noted in considering the operation of the present invention that the conductors 4, 5 of the cable 3 function as a path for radio frequency currents transmitted through the coupling M1, the radio frequency path including the conductors 9, I2 to an extension receiver unit, and impressing upon the input of a receiver, through the coupled coils 26, 24 the transmitted radio frequency energy, the radio frequency being selected by means of the uni-control selector 32, 30 and 25. The uni-directional potential path comprises a path which includes the lead 20, the conductor 4, the lead 9, the lead 36, the choke 35, the lead 34, the anode to cathode cells of tubes 22 and 23, the leads 38, 39 and 40, the lead I2', the lead I2, the conductor 5 and the lead 2| connected to the negative side of the filter I'I.

While I have indicated and described one arrangement for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. In combination, a radio frequency distribution system comprising a two wire transmission line, means for applying radio frequency currents across one end of said line, a source of direct current voltage connected across the same end of said line, a radio receiver located at a point remote from said end including a vacuum tube amplifier having grid and plate circuits, means for connecting said grid circuit to said transmission line comprising a transformer primary, a resistor and condenser connected in series to the high potential end of said primary winding and a conductive path connected between the end of said resistor which is remote from said condenser and the plate of said amplifier tube.

2. In combination, a radio frequency distribution system comprising a two wire transmission line, means for applying radio frequency currents across one end of said line, a source of direct current voltage connected across the said end of said line, a plurality of radio receivers connected to said line at separated points along the same, one of said receivers including a vacuum tube amplier having a cathode, grid and plate, a transformer having a secondary connected to said grid and cathode and a primary, means including a lead connecting the high potential end of said primary winding to one wire of said transmission line, a conductive connection between the plate of said amplifier tube and said lead and a variable resistor connected between the cathode of said amplifier and the low potential end of said primary winding for controlling the output volume of said receiver.

3. In combination, a two wire radio frequency transmission line, means for applying radio frequency voltage across one end of said line, a source of plate current connected to said transmission line and a plurality of receivers connected to said line at spaced apart points, at least one of said receivers comprising a vacuum tube amplier stage and a vacuum tube detector stage r il:

connected in cascade, each of said stages having plate and grid circuits, means including a transformer secondary winding and a primary winding for selectively tuning the grid circuit of said amplifier stage, a conductive connection including a radio frequency choke coil between the plates of said tubes and the high potential side of said transmission line and a condenser having one side connected to one end of said choke coil and its other side to one end of said transformer primary.

4. In combination a two wire grounded transmission line, means for applying radio frequency voltage across one end of said line, a source of plate voltage connected across said line and a radio receiver connected to said line at a point remote from said plate voltage source, said receiver comprising a vacuum tube amplifier stage and a vacuum tube detector stage each of said stages including a cathode, grid and plate, means for conductively connecting the plates of said tubes to the high potential side of said transmission line and separate resistors connected between the cathodes of said tubes and the grounded side of said transmission line arranged to provide suitable grid bias for said amplifier and detector stages.

5. In a radio frequency distribution system the combination of a two wire transmission line, means for applying radio frequency currents across one end of said line, a source of direct current voltage connected across the said end of said line, a plurality of radio receivers connected to said line at separated points along the same, at least one of said receivers including a vacuum tube amplifier having a cathode, a control grid, a. screen grid and a plate, a transformerhaving a secondary connected to said control grid and cathode and a primary, means including a lead connecting the high potential end of said primary winding to one wire of said transmission line, a. conductive connection between the screen grid and plate of said amplifier tube and said lead, and a variable resistor connected in series between said cathode and the low potential end of said primary winding.

ALVA R. HOPKINS. 

